Fluorine resins are fit for various uses because they have superior heat resistance, chemical resistance and the like in comparison with other resins. However the fluorine resins have disadvantages of poor adhesion and hydrophilicity, said disadvantages being attributable to the inactive surfaces of the fluorine resins.
Various processes for modifying the surfaces of the fluorine resins have hitherto been proposed. For example, E. R. Nelson et. al. (Ind. Eng. Chem., vol. 50, 1958, pp. 329-330) describe the use of a complex solution prepared from a tetrahydrofuran solution of metallic sodium and naphthalene. In this technique, not only it causes trouble from the viewpoint of working hygiene because the complex solution is unstable and liable to cause ignition during the treatment of the fluorine resins, but also adhesive property and the like of the modified surfaces of the fluorine resins decrease remarkably under the condition of sunlight exposure or high temperature.
Tsunoda et. al. [Kogyo Zairyo (Engineering Materials), vol. 29 (No. 2), 1981, p. 105] describe the use of a glow discharge. In this technique, a modification effect of the surfaces of the fluorine resins is remarkably inferior to that of nonfluorine resins such as polyethylene and the like.
Japanese Patent Publication (KOKOKU) No. 22108/1978 describes the use of a high frequency sputter etching under low pressure. In this method, there are several disadvantages that (i) a treating speed is slow, (ii) resinous residues formed during the sputter etching are deposited to inner parts of an expensive, large-sized treating apparatus with a vacuum system, and (iii) an abrasionable, irregular surfaces of the fluorine resins do not bring about sufficient adhesive properties and application properties of coatings for low fluidable adhesives, coatings and the like.
Japanese Patent Publication(KOKAI) No. 196834/1990 describes the use of laser beam in a special gaseous atmosphere such as B(CH.sub.3).sub.3 and Al(CH.sub.3).sub.3. According to this method, a treating speed is slow, and a strong poisonous gas and an expensive, large-sized treating apparatus are inevitably required.
Japanese Patent Publication (KOKOKU) No. 57143/1991 describes the use of excimer laser beam, said laser beam being directly irradiated to the fluorine resins. According to this technique, adhesive and wetting properties of the surfaces of the fluorine resins cannot sufficiently be improved.
Japanese Patent Publications No. 21928/1983 (KOKOKU), No. 127442/1990 (KOKAI) and No. 58375/1991 (KOKOKU) describe the use of plasma sputter etching at low temperature. In this method, it is difficult to obtain high adhesive strength because of the unchanged chemical composition of the treated surfaces of the fluorine resins. In order to achieve the same higher adhesive strength as that obtained according to the method by Nelson et. al., the surfaces of the fluorine resins must be treated for long-time under the narrow treating condition. Therefore said method is insufficient as an industrial treating technique.
Japanese Patent Publication (KOKAI) No. 125208/1993 discloses the method wherein ultraviolet laser beam is irradiated on the fluorine resins with which light-absorbing materials are kneaded previously. However this method cannot be applied to a surface modification of ready-made molded articles made of fluorine resins because the laser beam must be irradiated after a light-absorbing material is kneaded in the fluorine resins.
Japanese Patent Publication (KOKAI) No. 172560/1994 describes the method wherein an ultraviolet laser beam is irradiated on the fluorine resins in the presence of an inorganic silicon compound. When this method is applied to a modification of porous materials made of fluorine resins, there is a problem that the inorganic silicon compound remains in micropores of the porous materials.
Japanese Patent Application No. 258087/1993 describes the method wherein an aqueous pretreating liquid comprising an ultraviolet-absorbing compound and a fluorosurfactant is adhered on surfaces of molded materials made of fluorine resins, and ultraviolet laser beam is irradiated on the surfaces after drying. According to this method, wettability of the surfaces is not sufficiently improved, although adhesive properties of the surfaces are fairly improved.
Furthermore, the following methods are known: (a) the method wherein ArF excimer laser beam is irradiated on the fluorine resins which are immersed in hydrogen-containing liquid such as water, acids, alcohols and the like (Extended Abstracts No. 2, page 608 (The 54th Autumn Meeting. 1993); The Japan Society of Applied Physics); (b) the method wherein excimer laser beam is irradiated on the fluorine resin films immersed in water or aqueous solution of hydrogen peroxide or floating on said liquid (Japanese Patent Publication (KOKAI) No. 306346/1993). When these methods are applied to a modification of the porous materials, there is a problem that it is difficult to hydrophilize the inside of micropores owing to light scattering and absorption by the immersing liquid. Therefore it is impossible to filter the aqueous solutions of chemicals by means of the porous materials whose surfaces are modified by these methods, e.g. polytetrafluoroethylene film and the like.